1. Field of the Invention
This invention relates to flexible insulative substrates used to form elements such as amorphous silicon solar cells, thick and thin film circuits, and the like. It also relates to a method for making such substrates.
2. Description of the Prior Art
Known flexible insulative substrates used to form elements such as amorphous silicon solar cells include (1) substrates obtained by forming a thin film of silicon oxide or silicon nitride on a thin stainless steel plate, (2) substrates obtained by forming a layer of a resin such as polyimide on a thin stainless steel plate and subsequently a layer of titanium oxide, silicon oxide or silicon nitride on the resin layer by vacuum evaporation, and (3) thin flexible glass plate substrates.
However, the known substrates have the respective disadvantages. For instance, with the substrates (1) and (2), the stainless steel plate has to be finished to have a surface roughness below 0.1 .mu.m for the former substrate and a surface roughness below 0.5 .mu.m for the latter substrate. Otherwise, when the insulating covering layer is formed, a satisfactory insulative property cannot be assured. The substrates (2) may cause insulative failure because the resin layer is so low in hardness that it is apt to suffer defects thereon. Upon fabrication of an element on the substrate, the resin layer frequently generates a gas from the inside thereof though small in amounts with pinholes being left in the layer, causing an insulation failure. Although the substrate (3) has not such drawbacks as described above, it is so fragile that close attention must be paid to handling of the glass substrate. Otherwise, it would be broken.